When manufacturing vehicle body parts it is common to assemble larger components from multiple sheet metal parts which a shaped in a press and supplied to automatic assembly and welding lines operated by robotic devices. The robotic devices are required to pick a number of shaped sheet metal parts and place them in predetermined locations in a welding fixture. The parts are them clamped in place and spot welded together by a welding robot.
A problem with this arrangement is that the relative tolerances in the sheet metal parts to be assembled must be relatively large to allow robotic devices to locate the different parts in overlapping positions in a welding fixture. For instance, when locating two overlapping parts having hat-shaped cross-sections there is a risk of wedging as the parts are placed in the fixture. This can result in the assembly process being interrupted, until an operator can fix the problem, or in a deformed component and/or weakened weld as the wedged components are clamped together.
In order to avoid such problems it is possible to make the hat-shaped inner part relatively narrower than the outer hat-shaped part, in order to avoid wedging during assembly. A problem with this arrangement is that the internal gap or play between the assembled component parts does not allow welding to be performed along at least one of the opposed sides of the hat-shaped component. Further, when assembling two such parts, the relative height tolerances must be relatively narrow in order to ensure contact between both the side edges/flanges and the upper portions of the overlapping parts. If a gap occurs at either location, then this will result in a weakened weld.